A U.S. Senate report has concluded that the CIA used interrogation techniques against suspected terrorists that were “brutal” and “far worse” than they had led officials to believe, and that the methods failed to elicit accurate information.

The report by the U.S. Senate Intelligence Committee, released on December 9, said the use of the CIA's enhanced interrogation techniques "was not an effective means of obtaining accurate information or gaining detainee cooperation.”

The report detailed the CIA’s interrogation methods for suspected Al-Qaeda operatives at secret facilities in Europe and Asia in the years after the September 11, 2001 terrorist attacks against the United States.

It accused the CIA of misleading “policymakers and others” about the level of brutality used against suspected terrorists in the years following the attacks.

It said the methods included physical abuse that was conducted “despite warnings from CIA medical personnel” that the techniques “could exacerbate physical injuries.”

U.S. President Barack Obama called the revelations in the report "troubling" and said he banned torture after he took office in 2009 because it is "contrary to our values."

Obama said the techniques “did significant damage to America’s standing in the world and made it harder to pursue our interests with allies and partners.”

He said: “That is why I will continue to use my authority as president to make sure we never resort to those methods again.”

In a statement, CIA Director John Brennan said the agency made mistakes and learned from them.

But he also said the coercive techniques "did produce intelligence that helped thwart attack plans, capture terrorists and save lives."

A UN human rights expert said the report revealed a "clear policy orchestrated at a high level within the Bush administration" and called for prosecution of U.S. officials from the administration of the President George W. Bush who ordered systematic crimes against detainees.

Ben Emmerson, United Nations special rapporteur on human rights and counter-terrorism, said that senior Bush administration officials who planned and authorized crimes must be prosecuted, as well as CIA and other U.S. government officials who committed torture such as waterboarding.

Asked about the U.S. report, British Prime Minister David Cameron said, "Let us be clear: Torture is wrong. Torture is always wrong."

"After 9/11 there were things that happened that were wrong. And we should be clear about the fact they were wrong."

Polish Defense Minister Tomasz Siemoniak said the publication of the report will undermine the trust that its allies have in the United States.

The 6,000 page report was the result of a five-year investigation by the Senate Intelligence Committee, chaired by Democratic Senator Diane Feinstein.

Only an edited version of the report’s 525-page executive summary was published on December 9.

The CIA and senior U.S. administration officials have defended the interrogation techniques as effective and credited them with preventing numerous terrorist attacks they say were being planned.

Senior Republican lawmakers disputed the conclusion that the CIA interrogation methods highlighted in the report failed to yield intelligence leading to the capture of key terrorist figures.

Senate Republican Leader Mitch McConnell and Senator Saxby Chambliss, the intelligence committee’s ranking Republican member, said in a joint statement on December 9: “Claims included in this report that assert the contrary are simply wrong."

Shackled Naked

The two Republican senators echoed previous concerns voiced by critics of the decision to declassify and release the report to the public -- saying the move would have “serious consequences” for U.S. national security interests.

The report says detainees were forced to walk around naked and were “shackled with their hands above their heads for extended periods of times.

On other occasions, it said a detainee would be stripped by five CIA officers, then bound with tape and hooded.

The report says: “The detainee would then be hooded and dragged up and down a long corridor while being slapped and punched.”

One suspected Al-Qaeda operative known as Abu Zubaydah was subjected to “waterboarding,” a notorious simulated-drowning technique, on 83 separate occasions.

During one of these sessions, the report said Zubaydah became "completely unresponsive with bubbles rising through his open full mouth," but was later revived.

Other methods included confining detainees inside small boxes, isolating them for extended periods of time, threatening to kill detainees and telling them their relatives would be harmed, including with sexual assault.

George Tenet, who served as director of the CIA at the time of the September 11, 2001 terrorist attacks, told The Associated Press in an interview that the report was wrong to conclude that the CIA interrogation program failed to yield crucial intelligence about terrorist plots.

"We know that the program led to the capture of Al-Qaeda leaders and took them off the battlefield, that it prevented mass casualty attacks and that it saved thousands of American lives," Tenet said.

He compared the pressure to prevent another series of attacks to a “ticking time bomb every day."

Feinstein wrote that she understands “the CIA's impulse to consider the use of every possible tool to gather intelligence and remove terrorists from the battlefield,” and that the agency was encouraged by political leaders and the public to do whatever it could to prevent another attack.

“Nevertheless," Feinstein wrote in the report's foreword, "such pressure, fear, and expectation of further terrorist plots do not justify, temper, or excuse improper actions taken by individuals or organizations in the name of national security.”

Just hours before the report was released in Washington, U.S. Secretary of Defense Chuck Hagel announced that he had ordered a worldwide military "high alert" for U.S. forces due to the possibility that the report could lead to attacks against U.S. troops.

The White House said on December 8 that U.S. embassies and other sites around the world had been ordered to take precautions amid "some indications" of "greater risk."

In notices to Americans in Afghanistan and Pakistan, the U.S. embassies in the two countries are warning that the release of the report “could prompt anti-U.S. protests and violence against U.S. interests, including private U.S. citizens."